Write head tester using inductance

Abstract

A write head is tested by measuring the effect that magnetic fields have on the inductance of the write head. For example, a perpendicular write head may be placed in a magnetic field with a first angle, e.g., non-parallel and non-perpendicular, to the air bearing surface and the inductance is measured. After altering the angle of the magnetic field the inductance is again tested. In another embodiment, the angles may be parallel and perpendicular to the air bearing surface. The difference in the inductance value can be used to determine a characteristic of the write head, such as the presence of a recording pole. In some embodiments, the inductance may be measured while applying a bias current to the write head while the write head is in an external magnetic field.

What is claimed is: 
     
       1. A method comprising:
 A) applying a first magnetic field with a first polarity to a write head; 
 B) measuring a first inductance of the write head after the first magnetic field has been removed; 
 C) applying a second magnetic field with a second polarity to the write head, the second polarity being opposite the first polarity; 
 D) measuring a second inductance of the write head after the second magnetic field has been removed; 
 E) measuring a third inductance of the write head, wherein the third inductance is an initial inductance measured before the first magnetic field is applied to the write head; 
 F) using the first inductance, the second inductance, and the third inductance to determine hysteresis of the write head; and 
 G) recording the determined hysteresis of the write head. 
 
     
     
       2. The method of  claim 1 , wherein the write head is a perpendicular write head. 
     
     
       3. The method of  claim 1 , wherein the first magnetic field and the second magnetic field are parallel to a recording pole in the write head. 
     
     
       4. The method of  claim 1 , wherein the using the first inductance, the second inductance, and the third inductance to determine hysteresis of the write head comprises determining a variation of the first inductance and the second inductance from the third inductance and comparing the variation to a threshold. 
     
     
       5. The method of  claim 1 , further comprising applying to the write head and removing from the write head a fourth magnetic field and measuring a fourth inductance after the fourth magnetic field is removed, applying to the write head and removing from the write head a fifth magnetic field and measuring a fifth inductance after the fifth magnetic field is removed and using the fourth inductance and the fifth inductance with the first inductance, the second inductance, and the third inductance to determine the hysteresis of the write head. 
     
     
       6. The method of  claim 1 , wherein each of the applying a first magnetic field and the applying a second magnetic field is at least one of placing the write head in an external magnetic field and providing a bias current to the write head. 
     
     
       7. The method of  claim 1 , wherein each of the applying a first magnetic field and the applying a second magnetic field comprises providing a bias current to the write head to generate the first magnetic field and the second magnetic field, the method further comprising placing a magnetic film in physical contact with an air bearing surface of the write head, wherein magnetic flux of the first magnetic field and the second magnetic field generated by the write head is directed through the magnetic film. 
     
     
       8. An apparatus for testing a write head, the apparatus comprising:
 a means for applying and removing magnetic fields of opposite polarities in a write head; 
 an inductance meter configured to be coupled to the write head; and 
 a processor coupled to the inductance meter and the means for applying and removing magnetic fields, the processor configured to receive inductance measurements from the inductance meter, the processor comprising a computer-usable medium having computer-readable program code embodied therein for causing the processor to A) control the means for applying and removing magnetic fields to apply to the write head and remove from the write head a first magnetic field with a first polarity; B) control the inductance meter to measure a first inductance of the write head after the first magnetic field is removed; C) control the means for applying and removing magnetic fields to apply to the write head and remove from the write head a second magnetic field with a second polarity that is opposite the first polarity; D) control the inductance meter to measure a second inductance of the write head after the second magnetic field is removed; E) control the inductance meter to measure a third inductance of the write head, wherein the third inductance is an initial inductance of the write head measured before the first magnetic field is applied to the write head; F) determine hysteresis of the write head based on the first inductance, the second inductance, and the third inductance; and G) record the determined hysteresis of the write head. 
 
     
     
       9. The apparatus of  claim 8 , wherein the first magnetic field and the second magnetic field are parallel to a recording pole in the write head. 
     
     
       10. The apparatus of  claim 8 , wherein the code causing the processor to determine the hysteresis of the write head based on the first inductance, the second inductance, and the third inductance comprises determining a variation of the first inductance and the second inductance from the third inductance and comparing the variation to a threshold. 
     
     
       11. The apparatus of  claim 8 , wherein the code causes the processor to control the means for applying and removing a magnetic field to apply to the write head and remove from the write head a fourth magnetic field and to control the inductance meter to measure a fourth inductance after the fourth third magnetic field is removed, apply to the write head and remove from the write head a fifth magnetic field and to control the inductance meter to measure a fifth inductance after the fifth magnetic field is removed; the code further causes the processor to determine the hysteresis of the write head based on the measured inductances from the first inductance, the second inductance, the third inductance, the fourth inductance, and the fifth inductance. 
     
     
       12. The apparatus of  claim 8 , wherein the means for applying and removing magnetic fields of opposite polarities in the write head is at least one of a magnetic field generator that produces an external magnetic field that is applied to the write head and a write circuit configured to be coupled to a write element of the write head to provide a bias current to the write element that produces a magnetic field. 
     
     
       13. The apparatus of  claim 8 , wherein the means for applying and removing magnetic fields of opposite polarities in the write head comprises a write circuit configured to be coupled to a write element of the write head to provide a bias current to the write element that generates a magnetic field, the apparatus further comprising a magnetic film, an air bearing surface of the write head is placed in physical contact with the magnetic film so that magnetic flux generated of the magnetic field generated by the write head is directed through the magnetic film.